1. Field of the Invention
The present invention relates to a belt-type continuously variable transmission.
2. Description of the Related Art
In belt-type continuously variable transmissions, an endless belt is wound on an input-side primary pulley and an output-side secondary pulley that are provided in a housing and the rotation radius of the endless belt is varied by the two pulleys. The transmission gear ratio can be varied continuously.
In such belt-type continuously variable transmissions, the endless belt receives a heavy load and hence the endless belt needs to be sufficiently durable.
Needless to say, the durability of the endless belt strongly depends on the structure and the material of the belt itself. In addition, the durability is greatly influenced by the positions of the primary pulley and the secondary pulley, specifically, the relationship between the positions of a primary shaft and a secondary shaft of the respective pulleys in the axial direction. That is, if the primary shaft and the secondary shaft are not positioned correctly relative to each other in the axial direction, the endless belt is twisted and its durability is much lowered.
In the positioning of the primary shaft and the secondary shaft, first, one shaft is attached rotatably to the housing via a rolling bearing and its position in the axial direction is determined. Then, the other shaft is attached to the housing via a rolling bearing and its position in the axial direction is adjusted with respect to the one shaft by using a shim, a snap ring, or the like, whereby the primary shaft and the secondary shaft are aligned properly with each other in the axial direction.
Incidentally, the following method is conceivable to attach the primary shaft and the secondary shaft to the housing. For example, as shown in FIG. 3, a housing 200 is configured in such a manner as to be divided into a housing body 200a and a housing cover 200b and a bearing 220 for supporting a reference shaft 210 rotatably is fitted into the inside circumferential surface of a bearing mounting hole 230 of the housing cover 200b through which the shaft 210 is to penetrate. Then, the bearing 220 is held by pinching its outer ring from both sides in the axial direction by an end surface 230a of the housing cover 200b that is formed at one end (left end in FIG. 3) in the axial direction of the inside circumferential surface and a plate-like bearing retainer 240 that is fixed to an end surface of the housing cover 200b at the other end (right end in FIG. 3) in the axial direction.
However, to fix the bearing retainer 240 to the housing cover 200b, a plurality of screw holes should be formed in the bearing retainer 240 and joining bolts 250 are threadedly engaged with those screw holes through the housing cover 200b. In screwing the joining bolts 250, the bearing retainer 240 hides in the housing cover 200b and hence it is difficult to align the screw holes of the bearing retainer 240 with the corresponding insertion holes of the housing cover 200b. That is, the screwing of the joining bolts 250, that is, the fixing of the bearing retainer 240, cannot be performed easily.
Further, the bearing retainer 240 needs to be thick enough to allow formation of screw holes therein. The thick bearing retainer 240 causes the rolling bearing 220 to be bound strongly to the housing cover 200b, which is a factor of causing a phenomenon that the bearing 220 is deformed by thrust load from the pulley and the life of the transmission itself is shortened. To prevent such deformation of the bearing 220, it is necessary to make thinner the bearing retainer 240 that is in contact with the outer ring of the bearing 220 and thereby reduce its rigidity and hold the bearing 220 elastically with the bearing retainer 240. However, having a special sectional shape, such a bearing retainer 240 needs complex working and hence increases the cost.